Low energy availability in a lean endurance cyclist
A 27-year-old female road cyclist seeks help because she wants to lose 2 kg before a climbing race. She is 168 cm tall, weighs 54 kg, and has 12% body fat by skinfolds. She trains about 20 hours per week and estimates 900 kcal/day of exercise energy expenditure. Her typical intake is 1,800 kcal/day, with about 180 g carbohydrate. Resting metabolic rate is estimated at 1,350 kcal/day. She reports amenorrhea for 8 months, a metatarsal stress fracture 5 months ago, persistent fatigue, and ferritin of 18 µg/L. She believes that losing weight will improve her power-to-weight ratio and has already cut breakfast and post-training snacks. Her coach supports the weight loss. She asks whether a further 300–500 kcal/day deficit is reasonable.
1. Calculate her energy availability and interpret the result in context.
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Fat-free mass = 54 kg × 0.88 = 47.5 kg. Energy availability (EA) = (energy intake − exercise energy expenditure) / fat-free mass = (1,800 − 900) / 47.5 = 18.9 kcal/kg fat-free mass/day. This is below the commonly used optimal threshold of about 45 kcal/kg FFM/day and also below the 30 kcal/kg FFM/day level at which reproductive and bone effects become more likely. The calculation is an estimate because exercise expenditure and body composition are estimated, but the margin is large enough that the conclusion is robust: she has low energy availability. The combination of low EA, amenorrhea, prior stress fracture, low ferritin, and fatigue is consistent with relative energy deficiency in sport (RED-S), not simply 'good racing weight'. A further 300–500 kcal/day deficit would lower EA to roughly 12.6–16.8 kcal/kg FFM/day, worsening risk. The judgement is to reject the proposed deficit and treat energy availability as the clinical priority.
2. What carbohydrate and protein intakes would you recommend around training, and why not simply prescribe a higher total intake without changing timing?
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For a cyclist training about 20 hours per week, carbohydrate needs are high and should be periodised: roughly 6–10 g/kg/day depending on load, i.e. 324–540 g/day for 54 kg. Around key sessions, use 1–1.5 g/kg carbohydrate in the 1–3 hours before prolonged exercise, 30–60 g/hour during sessions longer than about 2 hours (and up to 90 g/hour with trained gut and multiple transportable carbohydrates), and 1–1.2 g/kg in the first hour after demanding sessions. Protein should be about 1.6 g/kg/day (86 g/day), spread as 20–30 g doses. Simply increasing total intake without timing may worsen gastrointestinal discomfort and leave low availability around training; timing supports performance, recovery, and appetite regulation. Address iron status with a clinician: ferritin 18 µg/L with fatigue warrants investigation and dietary iron counselling, not self-supplementation. The plan should increase total energy gradually, protect breakfast and post-training snacks, and monitor menstrual function, bone health, mood, and performance.
3. How would you respond to the athlete and coach about the requested 2 kg weight loss?
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Explain that the requested loss is not a neutral performance choice in her current state. At 54 kg and 12% body fat, further loss is likely to reduce fat-free mass and already-low energy availability rather than improve power-to-weight ratio. Use the RED-S framework: low EA can impair menstrual function, bone remodelling, iron status, immunity, recovery, and performance. State clearly that you cannot support an intentional deficit now; the immediate goal is restoring energy availability to at least about 30 kcal/kg FFM/day, and preferably toward 45 kcal/kg FFM/day, while maintaining training quality. Offer a shared plan: increase intake by about 300–500 kcal/day initially, add carbohydrate around sessions, reduce discretionary training if fatigue persists, and refer for menstrual and bone assessment. Involve the coach by framing the goal as availability and recovery, not weight. Agree on objective markers - menstrual return, ferritin, stress-fracture history, training response, and body composition only if clinically indicated - and document that weight loss was declined for safety reasons.